1. Field of the Invention
This invention relates to the initiation of explosive and pyrotechnic devices in aerospace and aeronautical devices and automotive vehicles.
2. Related Art
Explosive and pyrotechnic devices such as explosive bolts, bolt cutters, separation fairings, actuators, engine igniters, etc., are used in aeronautical and aerospace applications to perform various functions such as the separation of one structure from another, the release of a structure from a stowed position to a deployed position, etc. They are also used in the safety systems of land vehicles such as automobiles, for the deployment of air bags. Such devices are typically coupled to electrically operated initiators which, in response to suitable electrical signals, initiate the devices. The initiation signals are provided by electronic control devices for controlling and coordinating the initiation of a plurality of initiators connected thereto. The combination of a control unit, a plurality of initiators and an electrical communication system through which signals are sent from the controller to the initiators is referred to herein as an “ordnance firing system”.
In the prior art of aeronautical and aerospace devices such as missiles, satellites, launch vehicles, etc., and of land vehicle safety systems, the initiators in the ordnance firing systems that control the various explosive or pyrotechnic effectors (hereinafter referred to collectively as “reactive effectors”) typically comprise a hot bridgewire initiating element and an initiating charge of explosive or pyrotechnic material which is sensitive to the initiating element. In order to stimulate the hot bridgewire initiating element to release sufficient energy to ignite the ignition charge, a large amount of electrical energy (relative to what is generally required for most other functions on such devices) is required. For example, the firing of a hot bridgewire initiator typically requires a draw of ten amps from a 28-volt source for a period of about 0.1 second. Since there are often numerous effectors on a given device, the total energy requirement for initiation of the effectors far exceeds the energy requirement for operation of the circuitry that controls the device. For this reason, prior art ordnance firing systems typically include a dedicated high power energy source such as a thermal or chemical battery, for the purpose of providing sufficient energy to fire the hot bridgewires. The need in aerospace and aeronautical devices to provide such batteries, which are large and heavy, has been viewed as an unavoidable but significant burden. The batteries occupy space which could go to other, more useful components of the device or to increased payload capacity and, for airborne devices, they also increase the fuel consumption of the device at all times during flight.
Another feature of prior art ordnance firing systems is that all control functions affecting whether the effectors will function reside in a control system, from which command signals are forwarded to the effectors on dedicated wires.
U.S. Pat. No. 4,708,060 to Bickes, Jr. et al, dated Nov. 24, 1987 and entitled “Semiconductor Bridge (SCB) Igniter”, discloses SCB igniter elements, which are described as comprising an electrical semiconductor material disposed on a non-conductive substrate. The semiconductor material may be, e.g., a layer of n-type silicon that has been doped with phosphorus. As indicated in this Patent, other semiconductor materials and dopants can be used with similar effect. The resistivity of the doped material varies with the dopant level, as is well-understood in the art. Typically, the semiconductor material is disposed on the non-conductive substrate by a chemical vapor deposition process by which the thickness of the material can be precisely controlled. The surface of the non-conductive substrate is usually masked during the deposition process so that the layer of semiconductor material is rendered in an hourglass shape, i.e., it forms two relatively large pads joined together by a small bridge. Two pads of conductive material are then disposed upon the large pads of the semiconductor material and are separated by the bridge of semiconductor material between them. The resistivity of the semiconductor material and the dimensions of the semiconductor bridge between the conductive pads determines the effective resistance that the semiconductor bridge provides between the conductive pads. The Patent teaches a preference for SCBs of low resistance, e.g., no larger than 10 ohms, for safety reasons, i.e., in case the SCB is used with an electrostatic sensitive ignition charge (see column 7, lines 44-50) and for a reduction in resistivity with an increase in SCB size (see column 7, lines 53-55). The firing data provided pertain to high amperage (e.g., 10 amps and higher), short duration electrical initiation signals of less than 100 microseconds duration (see column 5, line 62 through column 6, line 3). The comparative data of Table 2 are difficult to interpret because SCB1 and SCB2 differ not only in resistance but also in thickness (2 micrometers vs. 4 micrometers).
U.S. Pat. No. 5,831,203 to Ewick, dated Nov. 3, 1998, discloses a high impedance semiconductor bridge detonator which illustrates, inter alia, that a SCB initiator element may be manufactured on a non-electrically conducting substrate using photolithographic masking, chemical vapor deposition, etc.
U.S. Pat. No. 4,976,200 to Benson et al, dated Dec. 11, 1990, discloses titanium bridge igniters.
U.S. Pat. No. 5,085,146 to Baginski, dated Feb. 4, 1992, discloses a planar, multi-layer low-energy initiation element.